Very nice effort! Well worth the download time...
I did something similar with the 2006 version of the SOS Children's Wikipedia CD and posted my experiences and challenges in the thread entitled Creating HUGE ebooks from the 2006 Wikipedia CD Selection
. I too had to locate my ebooks off-site ( see here
), due to the max. upload limit here.
I could contain everything within 1 ebook primarily since I reduced pictures to a max. image size (150x150) and max. color depth of 16 colors (4 bit). Without doing this, I too would have had to split the ebook to fit internal memory, but then I would lose some of the links pointing to the split .epub volumes.
Those pictures were too small, but allowed the final ebook size to be reduced! Also, reducing the color to 16 created some "banding" effects, but again drastically reduced the final ebook size. All in all, an acceptable compromise.
Try reducing your images to 4 bit .png (optimzed) i.e. 16 colours (or .jpg/.gif if smaller), then recreate the ebook to see the file size savings...
Did you try to create a version without ANY images (just rename your images folder temporarily to another name) just to see the min. ebook filesize?
Keep up the good work; I just love these gargantuan ebooks.